1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to a system to sense infrared radiation from a semiconductor chip and to methods of calibrating the same.
2. Description of the Related Art
Infrared thermal imaging is a common analysis technique used on semiconductor devices for failure analysis and design. In the past, typical thermal imaging of a functional device was done in an open air setup, that is, without any structures in the optical path of the detector. In such designs, air is used to cool the device undergoing testing. An open air setup is acceptable for parts that operate below certain power densities.
Some more recent designs of semiconductor devices exhibit much higher power densities. In some cases, more exotic cooling is required to keep the semiconductor device from failing due to thermal run away. Standard copper heat sinks used to cool the semiconductor devices in testing environments do not allow for optical access to the device itself. Yet optical access is required for thermal imaging.
One solution found in the industry for cooling a device with optical access is known as a diamond heat spreader. Since diamond is mostly transparent to the infrared spectrum, it is a good window material for thermal imaging. At the same time, the diamond can physically contact a device under test to spread and remove the heat during thermal imaging. In another conventional variant, a sealed fluid chamber is positioned on top of a semiconductor device. The fluid is infrared transparent and facilitates heat removal. The top of the chamber has a window made from an IR transparent material.
A difficulty with the conventional diamond spreader is the propensity for Newton's rings to degrade the infrared image of the semiconductor device. The Newton's rings appear due to inherent non-planarities in the upper surface of the semiconductor device and the lower surface of the diamond window. A difficulty with the conventional liquid setup is that the liquid and the upper window mask the actual count of photons emitted by the semiconductor chip. The liquid and the upper window both absorb and reflect percentages of any incident radiation, whether from the semiconductor chip, or in the case of the upper window, from both the semiconductor chip and the liquid. Without an accurate actual photon count from the semiconductor chip, a correct emissivity for the chip remains elusive.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.